1. Field of the Invention
The present invention relates to a process cartridge and an electrophotographic image forming apparatus using the same.
2. Related Background Art
Conventionally, in image forming apparatuses using an electrophotographic image forming process, there has been adopted a process cartridge system, in which an electrophotographic photosensitive member and a process means acting on the electrophotographic photosensitive member are integrated into a cartridge that is detachably mountable to a main body of an image forming apparatus. In the process cartridge system, maintenance on the apparatus can be conducted by a user himself without relying on a service man, thus achieving a substantial improvement in terms of operability. Thus, the process cartridge system is widely adopted in electrophotographic image forming apparatuses.
Among the electrophotographic image forming apparatuses are in-line type color electrophotographic image forming apparatuses in which a plurality of process cartridges are arranged in a row. There is available a contact development system, in which a developing roller as a developing member constituting a developing means of each of such cartridges is held in contact, for example, with a drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum, to effect development. To maintain a predetermined contact pressure between the developing roller and the photosensitive drum during image formation, the developing roller is urged against the photosensitive drum.
In case of this system, if the image forming apparatus is left unused for a long period of time with the process cartridges attached to the main body of the image forming apparatus, there is a fear of an elastic layer of each developing roller undergoing permanent deformation, thereby generating image unevenness during development.
As a construction for solving this problem, there have been proposed, in JP 2900530 B and JP 2001-337511 A, a process cartridge equipped with a mechanism for separating the photosensitive drum and the developing roller from each other when image forming operation is not being conducted, and an image forming apparatus using such a process cartridge.
Apart from this, as a charging means for charging the surface of the photosensitive drum of a process cartridge for forming images by electrophotography, a corona charger has been widely put into practical use. Corona charging is effective as a method of charging a surface to be charged uniformly to a predetermined electric potential. However, it requires a high voltage power source, and involves problems such as ozone generation due to corona discharge.
As a solution to this problem, there has been devised a contact charger for performing a charging process while keeping a charging roller as a charging member in contact with the surface of the photosensitive drum.
Like the developing roller, if left unused for a long period of time, this contact charger may involve permanent deformation of the elastic layer of the charging roller, resulting in generation of transversal streaks in the image at intervals corresponding to the charging roller cycle. Further, due to vibration, surfaces of the charging roller and the photosensitive drum may rub each other, which leads to generation of a local difference in potential, i.e., so-called rubbing memory in the surface of the photosensitive drum. This may also lead to generation of transversal streaks in the image at intervals corresponding to the charging roller cycle.
As means for avoiding this problem, JP 5-188667 A proposes a method according to which a member for separating the charging roller and the photosensitive drum from each other is held between them during shipment of the process cartridge, the member being removed by the user before using the cartridge. Further, U.S. Pat. No. 5,465,136 and JP 2000-181328 A propose a process cartridge or the like equipped with a mechanism which brings the charging roller, which has been kept separate from the associated photosensitive roller, into contact with it when the process cartridge is attached to the main body of the image forming apparatus.
Further, JP 2002-6722 A proposes a process cartridge in which the developing roller and the charging roller, held in the same unit, are kept apart from each other by means of a stopper or a spacing member until the process cartridge is put to use, and an image forming apparatus using such a process cartridge.